WFC3/UVIS Crosstalk and Crosstalk Correction

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Scientific paper

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Hubble Telescope, Hst, Wfc3, Wide Field Camera 3, Stsci

Scientific paper

We report the results of an analysis of crosstalk in on-orbit data taken with the WFC3/UVIS detector and provide a procedure to correct images for crosstalk. The WFC3/UVIS detector consists of two 2kx4k CCDs. Each CCD is read out simultaneously through two amplifiers, for a total of four amplifiers for the detector. As found during ground tests prior to launch (Baggett, 2009), electronic crosstalk between the amplifiers during readout induces faint, negative, mirror-symmetric ghost images in the other quadrant of the same CCD. Our analysis confirms that crosstalk on-orbit behaves as it did in pre-flight tests on the ground: the crosstalk ghost depends linearly on the strength of the offending signal and there is no crosstalk between the two CCDs. Based on a large set of on-orbit internal dark frames, we measure levels of -2.1*10-4 and -2.3*10-4 for crosstalk in quadrants B and D, respectively, and -0.6*10-4 and -0.8*10-4 for crosstalk in quadrants A and C, respectively. This means that for signal levels at full-well, the resulting crosstalk ghost values can reach about -15e-/pix in quadrants B and D, and about -5 e- /pix in quadrants A and C. Due to its mirror-symmetric behavior, crosstalk features will not co- add when combining dithered data acquired with sufficiently large offsets. However, for observers working with small dither-step data or with non-dithered data, we have developed a crosstalk correction procedure. We show that the algorithm successfully removes crosstalk features, restoring the pixels to a mean which is well within 1 σ of the mean of surrounding pixels. The standalone code, currently written in IDL, is available for use and can be downloaded from the WFC3 WWW site.

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